Preparation method of water-washing fly ash derived fuel

Abstract

The invention relates to a preparation method of a washing fly ash derived fuel, relates to the technical field of fuel preparation, and aims to effectively remove heavy metals and other harmful substances in waste incineration fly ash through washing treatment and simultaneously retain and extract combustible components in the fly ash. The method comprises the steps of fly ash collection and pretreatment, water washing treatment, solid-liquid separation, wastewater treatment, drying and screening, forming, fuel preparation and the like. By optimizing the temperature, time, pH value and other process parameters of water washing, the removal rate of harmful substances can be remarkably increased, and the solid fuel with high calorific value and low ash content can be prepared. In addition, wastewater generated in the treatment process can be recycled after being chemically treated, so that the consumption of water resources is further reduced. The method is simple in process and low in cost, has good environmental protection performance and economic benefits, is suitable for treating different types of waste incineration fly ash, and has wide application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of fuel preparation, and in particular to a method for preparing water-washed fly ash derived fuel. Background Art

[0002] Fly ash is a fine particulate matter produced during the incineration process of waste, which usually includes organic matter, heavy metals, dioxins, acid gases and other harmful substances that are not completely burned during the combustion process. The amount of fly ash produced is relatively large, and its composition is complex and has potential environmental hazards. If not properly handled and managed, the direct discharge or landfill of fly ash will cause serious pollution to the soil, water and atmosphere, and thus have a negative impact on the ecosystem and human health. Therefore, how to effectively handle and utilize fly ash has become an important issue in the waste incineration industry and the field of environmental protection.

[0003] Traditionally, fly ash treatment methods have focused on technologies such as solidification / stabilization, thermal treatment, and chemical treatment. Solidification / stabilization technology usually uses materials such as cement and lime to wrap or solidify fly ash, so that the heavy metals and harmful substances in it are fixed in a solid matrix, thereby reducing their migration in the environment. However, this method cannot completely eliminate harmful substances in fly ash, but only slows down their release rate by sealing. In addition, the volume of fly ash increases after solidification, which is not conducive to further resource utilization.

[0004] Thermal treatment technologies mainly include melting treatment and pyrolysis treatment. Melting treatment is to heat the fly ash at high temperature to melt and recrystallize it, so as to achieve the purpose of removing harmful substances. This method can effectively reduce the volume of fly ash and convert some components into usable slag or glass. However, melting treatment has high energy consumption, expensive equipment costs, and some difficult-to-control pollutants will still be generated during the treatment process. Pyrolysis treatment is to pyrolyze fly ash under oxygen-deficient or oxygen-free conditions to generate gas, liquid and solid products. Although pyrolysis technology has certain potential for resource utilization, its process is complex, costly, and requires strict control of reaction conditions.

[0005] Chemical treatment technology usually uses acid washing, alkaline washing or complexing agent treatment to remove heavy metals and other harmful substances in fly ash through chemical reactions. For example, acid washing technology can effectively remove heavy metals in fly ash, but a large amount of acidic waste liquid will be generated during the treatment process, which requires further treatment. In addition, secondary pollution may be generated during the acid washing process, such as the discharge of acid mist and waste acid solution, posing a new threat to the environment. Alkaline washing technology uses alkaline solution to dissolve some components in fly ash and remove harmful substances through precipitation, filtration and other means. However, the treatment effect of alkaline washing is greatly affected by the composition of fly ash and the concentration of alkaline solution, and the treatment effect is not stable enough.

[0006] In recent years, with the continuous improvement of environmental protection requirements and the increasing demand for resource utilization, fly ash resource treatment has become one of the key directions of research and application. Fly ash contains a certain amount of combustible components, such as unburned carbon and organic matter. If these components can be extracted and utilized through appropriate technical means, it can not only reduce the cost of harmless treatment of fly ash, but also achieve energy recovery and resource reuse.

[0007] At present, research on the resource utilization of fly ash mainly focuses on two aspects: one is to use fly ash as a raw material for building materials and convert it into building materials such as cement, concrete or bricks through appropriate processes; the other is to extract combustible substances from fly ash through physical or chemical means and use it as an alternative fuel or energy raw material. However, these methods still have some problems in practical applications. For example, the long-term stability and safety of fly ash products as building materials need to be further verified, and the method of extracting combustible substances faces challenges such as complex processes, low processing efficiency, and large equipment investment.

[0008] In this context, the present invention proposes a method for preparing a water-washed fly ash derived fuel, which aims to effectively remove harmful substances in fly ash through water washing treatment technology, while retaining and extracting the combustible components in fly ash, making it an efficient and environmentally friendly derivative fuel. Compared with traditional fly ash treatment methods, water washing treatment has the advantages of simple process, low cost, and environmental friendliness. By adjusting the process parameters such as temperature, time, pH value, etc. during the water washing process, the removal effect of harmful substances in fly ash can be optimized, and the combustible components can be retained to the maximum extent, so as to prepare a solid fuel with high calorific value and good combustion performance.

[0009] Specifically, the method of the present invention first performs preliminary screening and pretreatment on the fly ash to remove large particle impurities and non-combustible substances. Then, the fly ash is added to a certain proportion of water for water washing. During the water washing process, the pH value and stirring speed of the solution are adjusted so that the soluble salts, heavy metals and other harmful substances in the fly ash are fully dissolved and removed. After water washing, the fly ash is separated from the wastewater by solid-liquid separation technology to obtain washed fly ash and wastewater. After appropriate chemical treatment, the wastewater can be reused for washing the next batch of fly ash, further reducing the consumption of water resources. Finally, the washed fly ash is dried and screened, and an appropriate amount of adhesive is added to prepare it into a solid derivative fuel through processes such as briquetting or granulation.

[0010] The method of the present invention can not only effectively treat fly ash and reduce environmental pollution, but also realize energy recovery of fly ash through resource utilization, which has significant economic and environmental benefits. Through reasonable design and optimization of process parameters, the method for preparing water-washed fly ash-derived fuel of the present invention can be widely used in the treatment of different types of waste incineration fly ash, and has good application prospects and promotion value. Summary of the invention

[0011] The object of the present invention is to provide a method for preparing water-washed fly ash derived fuel to solve the problems raised by the above background technology.

[0012] To achieve the above object, the present invention provides the following technical solutions:

[0013] A method for preparing washed fly ash derived fuel comprises the following steps:

[0014] Fly ash collection and pretreatment: The fly ash collected during the waste incineration process is preliminarily treated to remove large particles of impurities and incombustible materials;

[0015] Water washing treatment: add the pretreated fly ash into water, with the mass ratio of water to fly ash being 2:1 to 10:1, stir and keep the water temperature between 30℃ and 60℃, and continue water washing for 1 to 4 hours;

[0016] Solid-liquid separation: After washing, the fly ash is separated from the water by centrifugation, sedimentation or filtration to obtain washed fly ash and wastewater;

[0017] Wastewater treatment: Chemical treatment of wastewater to precipitate heavy metals and other harmful substances, and then filter it to meet the standards for discharge or reuse;

[0018] Fly ash drying and screening: The washed fly ash is dried to a moisture content of less than 5%, and then screened to obtain fine ash containing high combustible components;

[0019] Molding and fuel preparation: The fine ash is mixed with the binder and then briquetted or pelletized to obtain solid derived fuel.

[0020] As a preferred technical solution of the present invention, the temperature of water in the water washing process is preferably 40° C. to 50° C. to improve the dissolution efficiency of soluble salts and some heavy metals in the fly ash and enhance the removal effect of harmful substances.

[0021] As a preferred technical solution of the present invention, the pH regulator used in the water washing process is sodium hydroxide or sodium carbonate, and its added amount is 0.1% to 0.5% of the total amount of water, so that the pH value of the solution is controlled between 7 and 8, preferably 7.5 to 8, to maximize the removal of heavy metals.

[0022] As a preferred technical solution of the present invention, during the water washing process, the mixture of fly ash and water is kept uniformly dispersed by a stirrer, and the stirring speed is controlled at 150 to 250 rpm to ensure that harmful substances in the fly ash are fully dissolved.

[0023] As a preferred technical solution of the present invention, a centrifugal separation device is used in the solid-liquid separation process, the centrifugal speed is controlled at 3000 to 5000 rpm, and the separation time is 5 to 15 minutes to ensure that most of the water in the fly ash is effectively removed.

[0024] As a preferred technical solution of the present invention, in the wastewater treatment process, the precipitant added to the wastewater is a mixture of calcium hydroxide and aluminum sulfate, the amount of calcium hydroxide added is 0.5% to 1.0% of the wastewater volume, and the amount of aluminum sulfate added is 0.1% to 0.5% to ensure effective precipitation of heavy metals and other harmful substances.

[0025] As a preferred technical solution of the present invention, the fly ash drying process is carried out in a vacuum drying oven, the drying temperature is controlled at 90°C to 110°C, and the drying time is 2 to 3 hours to minimize the residual moisture in the fly ash.

[0026] As a preferred technical solution of the present invention, the screening process uses a vibrating screen with a sieve hole size of 0.75 mm. The diameter of the fine ash particles after screening does not exceed 1 mm to ensure the uniformity and combustion performance of the molded fuel.

[0027] As a preferred technical solution of the present invention, the mixing process of the fine ash and the binder is carried out in a high-speed mixer with a mixing speed of 500 to 1000 rpm and a mixing time of 5 to 10 minutes to ensure that the binder is evenly distributed in the fine ash particles.

[0028] As a preferred technical solution of the present invention, the pressure in the briquetting or granulation process is controlled at 10 to 15 MPa, the molding time is 10 to 20 seconds, and the density of the solid derivative fuel is controlled at 1.0 to 1.2 g / cm 3 to ensure the strength and stability of the fuel.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The method for preparing water-washed fly ash derived fuel provided by the present invention can effectively remove heavy metals and other harmful substances in fly ash through a reasonable water-washing treatment process, thereby reducing the potential harm of fly ash to the environment. Compared with the traditional fly ash treatment method, the water-washing process adopted by the present invention is simple and easy to operate, has low cost, and can significantly reduce secondary pollution, and has good environmental performance.

[0031] In addition, the present invention can maximize the retention and extraction of combustible components in fly ash by optimizing process parameters such as temperature, time, and pH value during the water washing process, thereby preparing solid derivative fuel with high calorific value and good combustion performance. This fuel can be used in high-temperature equipment such as industrial boilers and kilns to replace traditional fuels, and has high economic value and energy utilization efficiency.

[0032] Finally, the method of the present invention also reduces the consumption of water resources through the recycling treatment of wastewater, further improving the environmental friendliness and economic feasibility of the process. Overall, the present invention not only achieves the harmless treatment of fly ash, but also realizes the energy recovery of fly ash through resource utilization, has significant economic and social benefits, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart of a method for preparing water-washed fly ash derived fuel proposed by the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1: Basic washed fly ash preparation method

[0036] Step 1: Fly ash collection and pretreatment

[0037] 50 kg of fly ash from a waste incineration plant was collected. First, a 2 mm sieve was used for preliminary screening to remove larger particles and incombustible substances. After screening, 45 kg of pre-treated fly ash was obtained.

[0038] Step 2: Washing

[0039] The pretreated fly ash was divided into two groups and added to 250 liters of water (water to fly ash mass ratio was 5:1). At 40°C, 0.5 kg of sodium hydroxide (0.2% of the water volume) was added and stirred at 200 rpm for 2 hours.

[0040] Step 3: Solid-liquid separation

[0041] The washed fly ash is separated from water by a centrifugal separation device, the centrifugal speed is set at 4000 rpm, the centrifugal time is 10 minutes, and wet fly ash with a water content of about 40% and 250 liters of wastewater are obtained.

[0042] Step 4: Wastewater Treatment

[0043] 0.75 kg of calcium hydroxide and 0.15 kg of aluminum sulfate were added to the wastewater, stirred evenly and left to stand for 2 hours to form a precipitate. After the precipitate was separated by filtration, the wastewater was further treated by sand filtration and activated carbon, and the treated water met the environmental discharge standards.

[0044] Step 5: Fly ash drying and screening

[0045] The wet fly ash was placed in a vacuum drying oven, the drying temperature was set at 100°C, the drying time was 2 hours, and after drying, dry fly ash with a moisture content of less than 5% was obtained, weighing about 22 kg. A 1 mm sieve was used for sieving, and 18 kg of fine ash was obtained.

[0046] Step 6: Molding and fuel preparation

[0047] The fine ash was mixed with 5% starch binder in a ratio of 95:5 for 8 minutes. The mixture was then put into a briquetting machine, with a pressure of 12 MPa applied for 15 seconds to obtain 20 pieces of solid fuel, each weighing 0.9 kg.

[0048] Results and Analysis

[0049] The density of the obtained solid derived fuel is 1.1 g / cm 3 , calorific value is 18MJ / kg, ash content is 38%. The fuel was tested in industrial boilers and showed good combustion performance, and the smoke emissions after combustion met the national environmental protection standards.

[0050] Example 2: Optimizing the method for preparing washed fly ash

[0051] Step 1: Fly ash collection and pretreatment

[0052] 50 kg of fly ash was collected from another city incineration plant and sieved through a 2 mm sieve to obtain 44 kg of pretreated fly ash.

[0053] Step 2: Washing

[0054] The fly ash was added to 220 liters of water (water to fly ash mass ratio of 5:1), and the water temperature was set to 45°C. 0.3 kg of sodium hydroxide was added to control the pH value of the solution to 7.8, the stirring speed was 250 rpm, and the washing time was extended to 3 hours.

[0055] Step 3: Solid-liquid separation

[0056] A centrifugal separation device was used with a centrifugal speed set at 4500 rpm and a centrifugal time of 12 minutes to obtain wet fly ash with a moisture content of about 35% and 220 liters of wastewater.

[0057] Step 4: Wastewater Treatment

[0058] 0.7 kg of calcium hydroxide and 0.12 kg of aluminum sulfate were added to the wastewater, stirred and left to stand for 3 hours to precipitate heavy metals and other harmful substances. After the precipitate was removed by filter press, the wastewater was sand filtered and treated with activated carbon and reused in the washing process of the next batch of fly ash.

[0059] Step 5: Fly ash drying and screening

[0060] The wet fly ash was placed in a drying oven at a drying temperature of 90°C for 2.5 hours, and finally 21 kg of dry fly ash was obtained. The 0.75 mm sieve was used to screen and 17 kg of fine ash was obtained.

[0061] Step 6: Molding and fuel preparation

[0062] The fine ash and organic resin binder were mixed in a ratio of 93:7 for 10 minutes. The mixture was then placed in a briquetting machine, with a pressure of 15 MPa applied for 18 seconds to obtain solid fuel blocks, each weighing 0.95 kg on average.

[0063] Results and Analysis

[0064] The density of the obtained solid derived fuel is 1.15 g / cm 3 The calorific value is 19MJ / kg and the ash content is 35%. In the combustion test in the industrial kiln, the combustion process is stable and the smoke emission is significantly reduced, showing good environmental friendliness.

[0065] Example 3: Effect of pH value on heavy metal removal during fly ash washing

[0066] Experimental design

[0067] Under the same conditions, different batches of fly ash were washed with water, and the effect on heavy metal removal was explored by adjusting the pH value of the solution. Four different pH values ​​of 6.5, 7.0, 7.5 and 8.0 were used in the experiment, and other parameters such as water temperature, mass ratio of water to fly ash, and stirring speed remained unchanged.

[0068] Experimental data

[0069]

[0070] Results Analysis

[0071] When the pH value is in the range of 7.5 to 8.0, the removal effect of heavy metals in fly ash is optimal, and the removal rate reaches more than 50%.

[0072] When the pH value is too low, the heavy metal removal effect is poor, and some organic matter in the fly ash may be dissolved by the acidic conditions, resulting in a decrease in fine ash production.

[0073] The calorific value and ash content did not fluctuate significantly during the pH change, but above pH 7.5, the environmental performance of the fuel improved.

[0074] Example 4: Effect of different stirring speeds on water washing effect

[0075] Experimental design

[0076] In order to study the effect of stirring speed on the water washing effect, this experiment set four stirring speeds of 100, 200, 300 and 400 rpm for water washing treatment respectively. Other conditions such as water temperature, pH value and mass ratio of water to fly ash remained unchanged.

[0077] Experimental data:

[0078]

[0079] Results Analysis

[0080] The stirring speed has a significant effect on the water washing effect. The higher the speed, the better the effect of removing soluble salts and heavy metals.

[0081] Above 300 rpm, the removal rate is significantly improved, and the quality and calorific value of fly ash fines remain at a high level.

[0082] The best effect is achieved when the speed reaches 400 rpm, but too high a stirring speed may increase energy consumption, so in actual operation it is necessary to balance the relationship between effect and energy consumption.

[0083] Example 5: Effect of different drying temperatures on fuel properties

[0084] Experimental design

[0085] The wet fly ash was dried under different temperature conditions. Three drying temperatures were set at 80°C, 100°C, and 120°C. The drying time was 2 hours, and other conditions remained unchanged.

[0086] Experimental data:

[0087]

[0088] Result analysis:

[0089] Drying temperature has a significant effect on the moisture removal effect of fly ash. The higher the temperature, the lower the moisture content of the fly ash.

[0090] At temperatures above 100°C, the calorific value and ash content of the fine ash after drying are significantly improved, and the density of the molded fuel is higher and the combustion performance is better.

[0091] Although excessively high temperatures (such as 120°C) can further improve fuel performance, they may lead to increased energy consumption and equipment loss, and need to be considered comprehensively.

[0092] Example 6: Industrial application test

[0093] Experimental design:

[0094] The solid derivative fuel treated under the above optimal conditions was subjected to actual application test in an industrial boiler to evaluate its combustion performance, smoke emission and thermal efficiency.

[0095] Test data:

[0096]

[0097]

[0098] Result analysis:

[0099] Test results show that solid derivative fuels have good combustion performance in industrial boilers, with a thermal efficiency of 85%, 10% higher than traditional fuels.

[0100] The emissions of smoke, NOx and SOx are all lower than the national standards, showing good environmental performance.

[0101] Through the above multiple embodiments, the present invention demonstrates the specific methods and effects of washing fly ash treatment and derivative fuel preparation under different conditions. The data of each embodiment show that the present invention can effectively remove harmful substances in fly ash and prepare solid fuel with high calorific value and good combustion performance, which has significant industrial application value and environmental protection significance.

[0102] The above embodiments are specific implementations of the present invention, and those skilled in the relevant technical field can make different changes and modifications based on the content of the present invention without departing from the spirit and scope of the present invention. Therefore, all equivalent implementations that do not depart from the spirit and scope of the present invention should be included in the protection scope of the present invention.

[0103] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in the field. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing washed fly ash derived fuel, characterized in that: The following steps are involved: Fly ash collection and pretreatment: The fly ash collected during the waste incineration process is preliminarily treated to remove large particles of impurities and incombustible materials; Water washing treatment: add the pretreated fly ash into water, with the mass ratio of water to fly ash being 2:1 to 10:1, stir and keep the water temperature between 30℃ and 60℃, and continue water washing for 1 to 4 hours; Solid-liquid separation: After washing, the fly ash is separated from the water by centrifugation, sedimentation or filtration to obtain washed fly ash and wastewater; Wastewater treatment: Chemical treatment of wastewater to precipitate heavy metals and other harmful substances, and then filter it to meet the standards for discharge or reuse; Fly ash drying and screening: The washed fly ash is dried to a moisture content of less than 5%, and then screened to obtain fine ash containing high combustible components; Molding and fuel preparation: The fine ash is mixed with the binder and then briquetted or pelletized to obtain solid derived fuel.

2. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: The temperature of the water in the water washing process is preferably 40° C. to 50° C. to improve the dissolution efficiency of soluble salts and some heavy metals in the fly ash and enhance the removal effect of harmful substances.

3. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: The pH value regulator used in the water washing process is sodium hydroxide or sodium carbonate, and the added amount is 0.1% to 0.5% of the total amount of water, so that the pH value of the solution is controlled between 7 and 8 to maximize the removal of heavy metals.

4. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: During the water washing process, the mixture of fly ash and water is kept uniformly dispersed by a stirrer, and the stirring speed is controlled at 150 to 250 rpm to ensure that the harmful substances in the fly ash are fully dissolved.

5. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: In the solid-liquid separation process, a centrifugal separation device is used, the centrifugal speed is controlled at 3000 to 5000 rpm, and the separation time is 5 to 15 minutes to ensure that most of the water in the fly ash is effectively removed.

6. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: During the wastewater treatment process, the precipitant added to the wastewater is a mixture of calcium hydroxide and aluminum sulfate, the amount of calcium hydroxide added is 0.5% to 1.0% of the wastewater volume, and the amount of aluminum sulfate added is 0.1% to 0.5% to ensure effective precipitation of heavy metals and other harmful substances.

7. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: The fly ash drying process is carried out in a vacuum drying oven, the drying temperature is controlled at 90° C. to 110° C., and the drying time is 2 to 3 hours to minimize the residual moisture in the fly ash.

8. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: The screening process uses a vibrating screen with a mesh size of 0.75 mm. The diameter of the fine ash particles after screening does not exceed 1 mm to ensure the uniformity and combustion performance of the briquette fuel.

9. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: The mixing process of the fine ash and the binder is carried out in a high-speed mixer at a mixing speed of 500 to 1000 rpm for 5 to 10 minutes to ensure that the binder is evenly distributed in the fine ash particles.

10. The method for preparing washed fly ash derived fuel according to claim 1, characterized in that: The pressure during the briquetting or pelletizing process is controlled at 10 to 15 MPa, the molding time is 10 to 20 seconds, and the density of the solid derivative fuel is controlled at 1.0 to 1.2 g / cm 3 to ensure the strength and stability of the fuel.

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